The present invention relates to a drive system of a wind turbine.
Drive trains for wind turbines are known and are used to convert the rotational energy of a wind rotor set in motion by the wind, into electrical energy by means of a generator coupled to the wind rotor. Herein, the wind rotor typically reaches rotary speeds in the region of approximately 10 to 20 min−1.
A large proportion of the existing wind turbines is equipped with rapidly rotating generators having a rotary speed of 1000 to 2000 min−1. In order to convert the relatively slow rotary speed of the wind rotor to the generator rotary speed, a three or more-stage transmission is connected therebetween which, in combination with the generator, is known in general as the drivetrain. The two drivetrain components are configured substantially independently from one another and are connected to one another via conventional couplings. This means that the drivetrain which in this case is designated a “non-integrated drivetrain”, comprises a gearing transmission with three or more gearing stages, a coupling and a generator, which are arranged in this order in the nacelle of the wind turbine behind the rotor shaft.
It is disadvantageous herein that the drivetrain requires a relatively large amount of space and due to the large number of components, has a complex structure.
Apart from this conventional gearbox solution, generators are also used which are coupled without a gearbox to the wind rotor. In this “direct drive” construction, the slowly running generator is driven directly by the wind rotor. A disadvantage herein is that due to the high torque that is conducted directly into the generator from the wind rotor, the generator and, in particular, the rotor of the generator have a comparatively large diameter. This is associated with relatively large dimensions and a large weight of the drivetrain.
A third concept provides for connecting a medium-speed generator and a transmission firmly to one another in a drivetrain component, in order to obtain a compact transmission-generator unit for wind turbines. A drivetrain of this type is described, for example, in EP 2 508 753 A1 (Siemens AG; Winergy AG) 10.10.2012. The drivetrain known from this published application for a wind turbine has a transmission with a transmission housing which is connected via a slowly rotating input shaft to a wind rotor. Furthermore, a generator is provided which has a generator housing which is firmly connected to the transmission housing. A rotor of the generator is driven via a sun gear shaft of the transmission. By means of the rotor rotating relative to a fixed generator stator, the rotational energy of the wind rotor is converted in a per se known manner into electrical energy by means of electrical induction. In modern wind turbines of this design, the gearing transmission is configured, for example, as a two-stage planetary gear set and the generator is configured, for example, as a permanent magnet generator.
The direct connection of the transmission to the generator leads to a substantial shortening of the drivetrain as compared with the “non-integrated drivetrain”. The coupling between the transmission and the generator is dispensed with in the medium-speed drivetrain and is replaced by similarly-acting connecting elements. Medium-speed systems require a smaller quantity of permanent magnets, as compared with permanent magnet direct-drives. The smaller dimensions as compared with conventional non-integrated drives and the lower weight of the medium-speed drives permit new nacelle configurations.
In all drivetrain configurations, roller bearings are one of the substantial causes of failures in a wind turbine.
For uses with a non-integral drivetrain, in the past, solutions have been developed for replacing the roller bearings with slide bearings.
For direct drives, according to the present state of the art, the use of slide bearings does not come into consideration or only to a very limited extent. A substantial reason for this is that in direct drives, the bearing diameter is so large that slide bearings exist or that slide bearings segmented in the peripheral direction must be used.
In medium-speed drives, particularly with a modular construction in which the generator is connected to the transmission in the form of a separate, enclosed component with the transmission, it is known to use slide bearings for the planet gears instead of conventional roller bearings. However, so far, the generators continue to be equipped with roller bearings so that significant expenditure must be made for the maintenance and serviceability of these roller bearings: to date, for modular construction medium-speed drivetrains, a separation point between the generator and the transmission has been provided. This separation point serves for the separability of both components in order to be able to separate the generator from the transmission in the event of a generator-side roller bearing damage.